Ah, but they're not telling us how thick the glass is, or exactly if it is glass after all. Impressive physical feats, no doubt, but there's also an element of "smoke and mirrors" as well as mechanical advantage in the form of leverage etc.

My guess is it's more a matter of how it hits, rather than how fast it hits.

It's possible to smash an entire pane of glass into little more than dust by throwing a small shard of ceramic at it - because ceramic shards are very hard and sharp, it's not actually too hard to achieve.

When doing exercise, the intent (whether you know it or not) is to cause damage to the muscles to get the body to repair them stronger, constantly pounding yourself in the head in addition to risking losing brain cells, will toughen the skull.

It's probably all "real". It's more a matter of technique and practice more than anything. By the time you can do similar stuff, it's not such a big deal. For example, alot of that stuff involves certain points of the body not prone to injury rather than actually strengthening the body.
The "chi" stuff is all just focus or mumbo jumbo for confidence(mental).

I can do some similar stuff and sometimes do, break boards, I elbow/ knee metal street posts etc. (It's all technique)
I learned in H.S. from a guy (Thai/Loatian) and he could break cinder-blocks out of walls and kick dead trees in half. Throw razor blades into stuff. Incredible to see.
When I asked where he learned I found out his uncle who taught him was the kick-boxing champion (Maui Thai) of Thailand. With the money he won, he moved here to USA!!!
I was pretty lucky, and obviously his style was useful in real fighting.
Later when I was older I had a roommate from Laos and found out he was an ex-Shoalin monk, same skills as vid.
They say the reason karate/other styles are better known is that their fighters one every year after year in contests. But when westerners were there to observe, their fighters were bribed a bunch to lose.
So it's not as well known.

I think so. People who know that stuff don't usually like to teach just anyone. For example the monks practice it only to protect thier temples. Or self /others from criminals.

I had moved to a rough city from a rural area. I saw the guy practice (privately) in the gym and kept bugging him. But he wouldn't show me anything. Then one evening I got jumped by three strangers and a broken jaw with a baseball bat.
So at school he told me come over and train with him every day for a while. At that time Jean Claude Van Damme movies were popular and the S.E. Asians were seeing their style in movies and knowing people would start to learn anyway.

There's lots of stories about the style but the language barrier is difficult sometimes. For example one style is said to come from a contest held each year, where if a criminal (from prison) could beat 50 men, he would be released.
It was more for amusement until one guy supposedly studied a cat. And also that to beat 50 men he'd have to use every body part as he'd get injured. So he won, got freed and started that style. (don't know the name due to translating difficulty). EDIT: Also, if you're young and you strike stuff over and over, you get stronger as it heals. But you learn how to strike so it won't hurt too.
When older people get injured, they don't always heal stronger.So the best guys probably learned from very young.